1. Field of the Invention
The present invention relates generally to an image forming apparatus having a self-repair system. More particularly, it relates to an image forming apparatus so adapted as to allow (self-diagnosis of the operating state and the like and) self-repair to be made utilizing artificial intelligence and knowledge engineering which have been studied extensively in recent years.
2. Description of the Prior Art
In the development field of precision instruments, industrial machines and the like, expert systems utilizing artificial intelligence (so-called AI) techniques have been studied extensively in recent years for the purpose of realizing labor saving in maintenance work and long-term automatic operation. The expert systems include one for making a self-diagnosis to judge whether or not an apparatus develops a fault and for making self-repair of the fault developed.
However, the conventional expert system (an automatic control system and a fault diagnosis system) is so adapted as to basically operate an actuator corresponding to a sensor on the basis of an output of the sensor. That is, one type of automatic control and fault diagnosis has been made by a predetermined combination of a sensor and an actuator. Accordingly, a certain sensor basically corresponds to a particular actuator, and the relationship therebetween has been stationary. Therefore, the conventional expert system has the following disadvantages:
(1) The relationship between parameters of the sensor and parameters of the actuator must be clearly expressed numerically. PA1 (2) From the reason mentioned in the above described item (1), the relationship between parameters of the sensor and parameters of the actuator depends largely on an object. Accordingly, the conventional expert system is lacking in versatility, that is, it cannot be utilized for a variety of objects. PA1 (3) The relationships between parameters of respective sensors and between parameters of respective actuators have no relation to control. Consequently, only simple control based on only the relationship between parameters of the sensors and parameters of the actuators which correspond to each other can be carried out, and faults which can be coped with are previously restricted so that unknown faults cannot be handled. PA1 (4) From the reason mentioned in the above described item (3), secondary effects exerted on parameters of other actuators which might be caused by the operation of an arbitrary actuator can not be anticipated.
Thus, in the conventional automatic control system and fault diagnosis system, only fault diagnosis based on sets respectively including independent sensors and actuators and fault repair based on the fault diagnosis have been made in such a manner that forecasting fault A is made on the basis of a set A of a sensor A and an actuator A, forecasting fault B is made on the basis of a set B of a sensor B and an actuator B, and forecasting fault C is made on the basis of a set C of a sensor C and an actuator C.
The applicant of the present application applied for a patent in connection with a new self-diagnosis and self-repair system for an image forming apparatus in which the disadvantages of the conventional system are overcome (see, for example, U.S. patent application Ser. No. 07/588,177).
The self-diagnosis and self-repair system for an image forming apparatus according to the prior application has two large features.
One of the features is that an objective machine is qualitatively expressed using parameters and fault diagnosis of the objective machine is made using the qualitative data, that is, fault diagnosis based on a qualitative model based system (hereinafter referred to as QMS) is made.
The other one is as follows: If QMS processing is performed, the results of fault diagnosis are hierarchically classified according to the "fault symptom" and the "fault", so that the results of the classification are stored as cases. Further, in many instances, common repair work is performed for a plurality of cases belonging to the same fault symptom and fault, so that work required for repair is expressed as the minimum unit in the rule form. A set of work units is registered as a work script, and is shared among the plurality of cases belonging to the fault symptom and the fault. A case based planning system (hereinafter referred to as "CBS") is generated utilizing a case base thus obtained. As a result, a case to which the current fault symptom and fault apply is selected from the cases hierarchically classified according to the fault symptom and the fault, and repair work is performed on the basis of the selected case and a work script corresponding to the case.
Meanwhile, in the prior invention, cases in the CBS are classified according to the "fault symptom" and the "fault". However, it is considered that the cases can be classified more finely. When a certain case is referred to, resulting in failure, the selection of a case belonging to the same class as a class to which the unsuccessful case belongs should be avoidable to improve the rate of success concerning selection of cases by classifying the cases more finely.
The inventors of the present application have paid attention to the detailing concerning classification of classes, to complete the present invention.